I create a light (but not too light) a wash with these colors. First I mix a light wash of cobolt blue as shown here. Then I add small amounts of Davy's Gray until I get a greenish gray color (see the photo below on the left).
I then add a tiny amount of purple lake until I have a gray with a slight purple hue. I realize it is hard to see the actual color in the photo below. Just be careful not over do it on the purple lake.
Once I achieve the suitable coloring I select my escoda 5/0 1212 Kolinsky watercolor brush to paint over my penciled lines around and in the area that I will be painting yellow. You will have to keep stirring the watercolor mixture to keep it from separating as you work. Don't worry if the lines are on the light side. Let dry and erase your pencil lines. You could actually cover all the pencil lines of your sketch should you desire as this color will blend in well.